This invention relates to a precombustion chamber for a diesel engine and more particularly to an improved cylinder head and prechamber insert construction.
In many types of engines, particularly diesel engines, there is provided in addition to the main combustion chamber a sub or precombustion chamber in which combustion is initiated. The combustion from this prechamber then causes the mixture in the main chamber to ignite and normally some form of throat section interconnects the prechamber and the main chamber and through which the hot gases may emanate.
Although these types of constructions provide very good performance under all running conditions, the actual formation of the cylinder head and prechamber cause some problems. Specifically, in addition to forming a main combustion chamber surface, the interior of the cylinder head must be formed with the prechamber and the relatively narrow throat that connects the prechamber to the main chamber. It is not practical for a variety of reasons to form the cylinder head as a single unitary construction when a prechamber is employed. The reason for this is if the casting and machining techniques become very difficult due to the small throat that interconnects the prechamber with the main chamber.
Therefore, it has been the practice to form at least a portion of the prechamber in a cylinder head casting and to use a prechamber insert that is fixed somehow to the cylinder head and which forms the lower end of the prechamber and the throat which connects the prechamber to the main chamber.
Obviously, such multiple part constructions give rise to difficulties in assembly and maintaining the components together. For example, it could be disastrous to the engine if the insert piece were to fall out of the cylinder head during the engine operation. In addition, it is normally the practice to form the insert piece from a different material than the main cylinder head material and this gives rise to additional problems caused by uneven thermal expansions and cooling rates.
One way in which the insert piece has been affixed to the cylinder head is to form the insert piece and have it extend through an opening in a mating surface of the cylinder head. This insert piece is then held in place by a cap installed on the outside of the cylinder head. However, this type of construction presents considerable problems in conjunction with sealing since it is necessary to seal the insert piece and cylinder head around the entire opening in which the insert piece is received.
Another type of construction is shown in FIG. 1 of the drawings and this employs a multiple part construction. As may be seen in this figure, a portion of a diesel engine is illustrated and is identified generally by the reference numeral 11. This diesel engine 11 includes a cylinder block 12 having a cylinder bore 13 formed by an inserted liner 14. A piston 15 reciprocates in the cylinder bore 13 and drives a crank shaft (not shown) in a well known manner.
A cylinder head assembly, indicated generally by the reference numeral 16 is affixed to the cylinder block 12 in a known manner and this cylinder head assembly 16 includes a lower casting 17 that has a lower surface 18 that sealingly engages a cylinder head gasket 19 so as to provide a seal around the cylinder bore 13. A counterbored opening 21 is formed in the cylinder head casting 17 with its larger bore at the upper end and its smaller bore at the lower end where the main combustion chamber 22 is formed. A shoulder 23 is formed between these bore sections and an insert piece, indicated generally by the reference numeral 24, has two diameter sections terminating in a downwardly facing shoulder 25 that is abuttingly engaged with the cylinder bore shoulder 23 so as to fix the vertical location of the insert piece 24. The insert piece 24 is formed with a recess 26 which forms in part a precombustion chamber, indicated generally by the reference numeral 27. This prechamber recess 26 is offset to one side of the main combustion chamber 22 and is connected to it by a throat section 28 that extends generally to the center of the combustion chamber 22.
An upper cylinder head piece 29 is affixed to the lower cylinder head casting 17 and has a spherical section 31 which cooperates with the insert recess 26 to complete the formation of the prechamber 27 and so as to lock the insert piece 24 into position in the cylinder head portion 17.
A glow plug 32 and fuel injector 33 are supported in the upper cylinder head member 29 and project into the prechamber recess 27 for providing heat for initiating combustion at least during start up and for spraying fuel into the prechamber 27 and main combustion chamber 22 through the throat 28.
The engine 11 is also water cooled and this involves the formation of a cooling jacket 34 in the cylinder block, a coolant passage 35 in the lower cylinder head member 17 and a coolant jacket 36 in the upper cylinder head 29.
It should be readily apparent from this construction that there are a number of sealing surfaces which must be properly sealed both for water and compression purposes. In addition, the number of parts and complexity of the engine obviously increases.
It is, therefore, a principal object of this invention to provide an improved cylinder head structure forming a precombustion chamber which can minimize the number of parts and the effects of thermal differences.